Surface borided SAE 1020 steel with dual phase core microstructure

Abstract

In the present study, the production of dual phase steel structure in the core of surface borided SAE 1020 steel and the effect of martensite volume fraction (MVF) on tensile, microhardness and microstructure were investigated. For the purposes, specimens were divided into two groups. The first group of specimens was subjected to intercritical annealing at temperatures between 720 and 820°C. Specimens from the second group were first borided at 900°C for 2 h, and then without removing the specimens from the furnace, they were annealed at different intercritical heat treatment temperatures from 720 to 820°C. During the intercritical annealing process, the specimens of both groups were kept in the furnace for 30 min. Thermal processes were followed by microstructural analysis of the specimens. The MVFs of the specimens were calculated after intercritical annealing. Heat treatment temperatures that resulted in common MVFs were found for the two groups. In the first and second groups of specimens, dual phase microstructures were obtained after heat treatment. Up to 83 μm thick boride layer was obtained on the surface of the borided specimens, and a ferrite–martensite microstructure was produced in the matrix. In addition, an X-ray diffraction test was applied to the borided specimens. According to microhardness tests, a hardness value of up to 1530 was obtained on the boride layer.